Fungicides have myriad uses, including for crop protection; as food, feed, and cosmetics preservatives; and as therapeutic agents for both human and veterinary applications. Crop yield reduction, foodborne diseases and fungal infections of both humans and animals are a problem in both developed and developing countries.
Synthetic insecticides or fungicides often are non-specific and therefore can act on organisms other than the target ones, including other naturally occurring beneficial organisms. Because of their chemical nature, they may also be toxic and non-biodegradable. Consumers worldwide are increasingly conscious of the potential environmental and health problems associated with the residuals of chemicals, particularly in food products. This has resulted in growing consumer pressure to reduce the use or at least the quantity of chemical (i.e., synthetic) pesticides. Thus, there is a need to manage food chain requirements while still allowing effective pest control.
A further problem arising with the use of synthetic insecticides or fungicides is that the repeated and exclusive application of an insecticide or fungicides often leads to selection of resistant pathogenic microorganisms. Normally, such strains are also cross-resistant against other active ingredients having the same mode of action. An effective control of the pathogens with said active compounds is then not possible any longer. However, active ingredients having new mechanisms of action are difficult and expensive to develop.
The risk of resistance development in pathogen populations as well as environmental and human health concerns have fostered interest in identifying alternatives to synthetic insecticides and fungicides for managing plant diseases. The use of biological control agents is one alternative.
Non-ribosomal peptides, such as the fusaricidins, are well-recognized for their antimicrobial properties and have been used in the field of crop protection. Because of their mode of action, they also have potential uses in biopharmaceutical and other biotechnology applications. Fusaricidins can be isolated from Paenibacillus sp. and have a ring structure composed of 6 amino acid residues in addition to 15-guanidino-3-hydroxypentadecanoic acid. Fusaricidins isolated from Paenibacillus polymyxa include LI-F03, LI-F04, LI-F05, LI-F07 and LI-F08 (Kurusu K, Ohba K, Arai T and Fukushima K., J. Antibiotics, 40:1506-1514, 1987) and additional fusaricidins A, B, C and D have been reported (Kajimura Y and Kaneda M., J. Antibiotics, 49:129-135, 1996; Kajimura Y and Kaneda M., J. Antibiotics, 50:220-228, 1997).
Certain fusaricidins are known to have germicidal activity against plant pathogenic fungi such as Fusarium oxysporum, Aspergillus niger, Aspergillus oryzae and Penicillium thomii. Some fusaricidins also have germicidal activity against Gram-positive bacteria including Staphylococcus aureus (Kajimura Y and Kaneda M., J. Antibiotics, 49:129-135, 1996; Kajimura Y and Kaneda M., J. Antibiotics, 50:220-228, 1997). In addition, it has been found that specific fusaricidins have antifungal activity against Leptosphaeria maculans which causes black root rot of canola (Beatty P H and Jensen S E., Can. J. Microbiol., 48:159-169, 2002). There is a need to further characterize the fusaricidin compounds and identify strains of Paenibacillus sp. that produce those fusaricidins providing a broad spectrum of antifungal activity at relatively low application rates.
Fusaricidins and other antifungal metabolites may be obtained through fermentation of Paenibacillus sp. However, many Paenibacillus sp. strains also produce antibiotics known as polymyxins. Polymyxins are selectively toxic to Gram-negative bacteria and may have a neurotoxic or nephrotoxic effect when given to human patients. The global problem of advancing antimicrobial resistance and the relative toxicity of the polymyxins require careful use and administration of these antibiotics. For this reason it is highly desirable that a Paenibacillus sp. strain developed for use in agriculture express relatively high levels of the fusaricidins and no detectable polymyxins. Such a strain would pose little or no risk to workers and consumers. In addition, there is a need to identify Paenibacillus sp. strains that exhibit a broad spectrum of activity. Improvements to the efficacy of existing fungicides, especially those that are not susceptible to development of fungal resistance, are highly desirable.